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    <meta charset="UTF-8" />
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    <title>Document</title>
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  <body>
    <script>
      //找出数组中 元素为10的下标，有则打印该下标，没有则打印-1
      let arr = [88, 20, 10, 100, 50]
      let j = -1
      for (i = 0; i < arr.length; i++) {
        if (arr[i] === 10) {
          j = i
          break
        }
      }
      console.log(j)
    </script>
  </body>
</html>
